Mark Estorga, 564th Aircraft Maintenance Squadron director, describes the programmed depot maintenance process for the KC-135 Stratotanker aircraft to the Hon. Ellen Lord, under secretary of defense for acquisition and sustainment. Lord visited Tinker Air Force Base, Oklahoma, on Aug. 18, 2020, to get an understanding of the Air Force Sustainment Center mission. (U.S. Air Force photo by Paul Shirk)